Cadherins are a rapidly expanding superfamily of calcium-dependent cell adhesion molecules (CAMs) (for review, see Munro et al., In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17-34, RG Landes Co., Austin Tex., 1996). All cadherins appear to be membrane glycoproteins that generally promote cell adhesion through homophilic interactions (a cadherin on the surface of one cell binds to an identical cadherin on the surface of another cell), although cadherins also appear to be capable of forming heterotypic complexes with one another under certain circumstances and with lower affinity.
There are many different types of cadherins. The most extensively studied group of cadherins is known as the classical, or type I, cadherins. Classical cadherins have been shown to regulate epithelial, endothelial, neural and cancer cell adhesion, with different cadherins expressed on different cell types. All classical cadherins have a similar structure. As illustrated in FIG. 1A, classical cadherins are composed of five extracellular domains (EC1-EC5), a single hydrophobic domain (TM) that transverses the plasma membrane (PM), and two cytoplasmic domains (CP1 and CP2). The calcium binding motifs DXNDN (SEQ ID NO:1), DXD and LDRE (SEQ ID NO:2) are interspersed throughout the extracellular domains, and each 110 amino acid region that contains such motifs is considered a cadherin repeat The first extracellular domain (EC1) contains the cell adhesion recognition (CAR) sequence, HAV (His-Ala-Val), along with flanking sequences on either side of the CAR sequence that play a role in conferring specificity. Synthetic peptides containing the HAV sequence and antibodies directed against such peptides have been shown to inhibit classical cadherin-dependent processes (Munro et al., supra; Blaschuk et al., J. Mol. Biol. 211:679-82, 1990; Blaschuk et al., Develop. Biol. 139:227-29, 1990; Alexander et al., J. Cell. Physiol. 156:610-18, 1993).
Cadherins that contain calcium binding motifs within extracellular domain cadherin repeats, but do not contain an HAV CAR sequence, are considered to be nonclassical cadherins (illustrated in FIGS. 1B to 1AA). To date, nine groups of nonclassical cadherins have been identified (types II-X). These cadherins are also membrane glycoproteins. Type II, or atypical, cadherins include OB-cadherin (cadherin-11; see Getsios et al., Developmental Dynamics 211:238-247, 1998; Simonneau et al., Cell Adhesion and Communication 3:115-130, 1995; Okazaki et al., J. Biological Chemistry 269:12092-12098, 1994), cadherin-5 (VE-cadherin; see Navarro et al., J. Cell Biology 140:1475-1484, 1998), cadherin-6 (K-cadherin; see Shimoyama et al., Cancer Research 55:2206-2211, 1995; Shimazui et al., Cancer Research 56:3234-3237, 1996; Inoue et al., Developmental Dynamics 211:338-351, 1998; Getsios et al., Developmental Dynamics 211:238-247, 1998), cadherin-7 (see Nakagawa et al., Development 121:1321-1332, 1995), cadherin-8 (see Suzuki et al., Cell Regulation 2:261-270, 1991), cadherin-12 (Br-cadherin; see Tanihara et al., Cell Adhesion and Communication 2:15-26, 1994), cadherin-14 (see Shibata et al., J. Biological Chemistry 272:5236-5240, 1997), cadherin-15 (M-cadherin; see Shimoyama et al., J. Biological Chemistry 273:10011-10018, 1998), and PB-cadherin (see Sugimoto et al., J. Biological Chemistry 271:11548-11556, 1996). For a general review of atypical cadherins, see Redies and Takeichi, Developmental Biology 180:413-423, 1996 and Suzuki et al., Cell Regulation 2:261-270, 1991.
Types III-X include LI-cadherin (type III; see Berndorff et al., J. Cell Biology 125:1353-1369, 1994). T-cadherin (type IV; see Ranscht, U.S. Pat. No. 5,585,351; Tkachuk et al., FEBS Lett. 421:208-212, 1998; Ranscht et al., Neuron 7:391-402, 1991; Sacristan et al., J. Neuroscience Research 34:664-680, 1993; Vestal and Ranscht, J. Cell Biology 119:451-461, 1992; Fredette and Ranscht, J. Neuroscience 14:7331-7346, 1994; Ranscht and Bronner-Fraser, Development 111:15-22, 1991), protocadherins (type V; e.g., protocadherins 42, 43 and 68; see Sano et al., EMBO J. 12:2249-2256, 1993; GenBank Accession Number AF029343), desmocollins (type VI; e.g., desmocollins 1, 2, 3 and 4; see King et al., Genomics 18:185-194, 1993; Parker et al., J. Biol. Chem. 266:10438-10445, 1991; King et al., J. Invest. Dermatol. 105:314-321, 1995; Kawamura et al., J. Biol. Chem. 269:26295-26302, 1994), desmogleins (type VII; e.g., desmogleins 1 and 2; see Wheeler et al., Proc. Natl. Acad. Sci. USA 88:4796-4800; Koch et al., Eur. J. Cell. Biol. 55:200-208, 1991), and cadherin-related neuronal receptors (type X; see Kohmura et al., Neuron 20:1137-1151, 1998).
Most studies of nonclassical cadherins have focused on atypical or type II cadherins. The structure of these cadherins is similar to that of the type I cadherins, but they do not contain the CAR sequence, HAV (FIG. 1B). Furthermore, functions mediated by the atypical cadherins may be diverse. OB-cadherin, which is also known as cadherin-11, is an atypical cadherin (Getsios et al., Developmental Dynamics 211:238-247, 1998; Okazaki et al., J. Biol. Chem. 269:12092-98, 1994; Suzuki et al., Cell Regulation 2:261-70, 1991; Munro et al., supra). This cadherin can promote cell adhesion through homophilic interactions. Recent studies have shown that OB-cadherin is not expressed by well-differentiated, poorly invasive cancer cells, whereas it is expressed by invasive cancer cells (et al., Cancer Res. 56:3234-37, 1996; Shibata et al., Cancer Letters 99:147-53, 1996). OB-cadherin levels are also high in stromal cells and osteoblasts (Shibata et al., Cancer Letters 99:147-53, 1996; Simonneau et al., Cell Adhes. Commun. 3:115-30, 1995; Matsuyoshi and Imamura, Biochem. Biophys. Res. Commun. 23:355-58, 1997; Okazaki et al., J. Biol. Chem. 269:12092-98, 1994). Collectively, these observations have led to the hypothesis that OB-cadherin may mediate the interaction between malignant tumor cells and other cell types, such as stromal cells and osteoblasts, thus facilitating tumor cell invasion and metastasis.
OB-cadherin is expressed in certain specific cell types. In some invasive cancer cells, OB-cadherin is not only found at sites of cell-cell contact, but also in lamellopodia-like projections which do not interact with other cells. These observations suggest that OB-cadherin may also play a role in modulating cell-substrate interactions. In adipocytes, OB-cadherin is the only known expressed cadherin. OB-cadherin is therefore likely to mediate adhesion between adipocytes, and it is likely to be an important regulator of adipogenesis. Another cell type that expresses OB-cadherin is the pericyte (also known as the peri-endothelial cell). Pericytes are contractile cells which are similar to smooth muscle cells. They encircle the endothelial cells of blood vessels. Pericytes are involved in maintaining the structural integrity of blood vessels (Hanahan, Science 277:48-50, 1997; Lindahl et al., Science 277:242-245, 1997). Loss of pericytes causes blood vessels to regress.
Other atypical cadherins appear to have different functions. For example, cadherin-5 (also referred to as VE-cadherin) appears to be involved in endothelial cell adhesion and cadherin-6 (also referred to as K-cadherin) may be involved in embryonic kidney cell adhesion and is up-regulated in kidney cancer. Cadherin-15 also appears to play a role in the terminal differentiation of muscle cells.
Notwithstanding these recent advances, nonclassical cadherin function remains poorly understood at the biological and molecular levels. Accordingly, there is a need in the art for identifying sequences involved in modulating nonclassical cadherin-dependent functions, such as cell adhesion, and for the development of methods employing such sequences to inhibit processes such as cancer cell adhesion, invasion and metastasis. The present invention fulfills these needs and further provides other related advantages.